Ultrasonic delay lines



Jan. 15, 1957 D QI ,ARIENBERG ETAL 2,777,997

ULTRASCNICYDELAY'LINES- Filed Nov 6, 1951" FIG. 2

l NTORS DAVID L. NBERG ROBERT M. ASHBY ATTORNEY Unite States PatentULTRASONIC DELAY LINES David L. Arenberg, Rochester, Mass., and RobertM. Ashby, Pasadena, Calif.

Application November 6, 1951, Serial No. 255,128

23 Claims. (Cl. 333-30) (Granted under Title 35, U. S. Code (1952), see.266) Thi invention relates in general to the art of delaying in time,electrical signal transmission, and more particulariy to ultrasonicdelay lines employing multiple reflections of a directed acousticalbeam.

In the electronic art, it is frequently desirable to delay signaltransmission for periods of time ranging up to several milliseconds induration. It is usually not feasible to employ electromagnetic delaylines for delays of such magnitudes especially with short pulse signalsrequiring wide band-widths. To attain a longer delay time than ispossible with comparable electromagnetic delay lines, various types ofultrasonic delay lines have come into general use. These ultrasonicdelay lines operate as follows: The signals to be delayed a small,finite time are caused to modulate a high frequency carrier. Thefrequency of the latter signal may be of the order of several megacyclesper second. This modulated high frequency signal is converted to anacoustical (sound) signal which is made to traverse a given path asultrasonic energy. At the end of this path, some or all of theacoustical energy is reconverted to electrical energy, amplified anddetected to yield the original modulation signal. The relatively lowvelocity of propagation of sound Within the delay line results in longerdelay times in this type than is possible with electromagnetic delaylines. The delay time in such an ultrasonic delay line is proportionalto the total path length from the input to the output of the device.

Even with the relatively low velocity of the propagation of sound, itfrequently happens that the path length required is so great that it isdifficult or impractical to construct a delay line having a singlestraight path from the input to the output. To reduce the over-alllength of ultrasonic delay lines, for the longer delay times, tubescontaining a liquid propagation medium have been arranged in variouspatterns with reflectors placed at the junctions of the tubes to directthe energy from one tube to another. Delay lines of this type have arelatively large size, are relatively difficult to construct, and aresubject to leakage of the propagation medium.

A second type of delay line using multiple reflection paths consists ofa tank containing a liquid propagation medium with reflectors placed atcertain points in the tank and in the path of the ultrasonic beam. Thesereflectors cause the ultrasonic beam to traverse the length and width ofthe tank a number of times before arriving at the output of the delayline. Delay lines of this type are also diflicult to construct, arefrequently unstable in their operation, and are apt to produce unwantedsignals due to the fact that multiple reflections in the medium presentalternative paths for the reflected beam.

A third type of delay line using multiple reflection paths consists ofeither rectangular solids or rectangular forms containing a liquidpropagation medium wherein a beam of energy is introduced at one cornerof the rectangle and is directed at a point on the rectangle wall closeto the corner opposite the point of introduction. Reflection of the beamtakes place and a path is 2,777,997 Patented Jan. 15, 1957 traced acrossthe last-mentioned corner to another wall of the rectangle. A secondreflection takes place at this point and the beam is reflected back to apoint on a Wall of the rectangle close to the corner where the beamoriginated. Successive reflections continue until the path traced by thebeam comprises two series of parallel lines diagonally disposed acrossthe rectangle, with'one series of lines being perpendicular to the otherseries, the path terminating at a corner adjacent to the original cornerin a suitable receiver. Delay lines of this type are said to haverectangular symmetry. The primary disadvantage of a rectangularlysymmetrical design is that reflection must take place several times fromany given wall of the structure to provide sufficient path length. Foreflicient use of the delaying medium, successive points of reflection oneach wall must necessarily be closely spaced. Since the energy is notusually confinable to a beam of small diameter because of diffractioneffects, the desired energy path is not followed by all of the energy.Some paths are of greater or shorter length than the desired path. Theultimate result i that the major signal reaching the receiver isaccompanied by several unwanted or secondary signals.

Therefore, it is an object of. the present invention to provide a delayline employing multiple reflection paths which is of particularlycompact, simple, and rugged mechanical construction and which hascomparatively small secondary signals.

A further object of theinvention is to provide a delay line which islight in weight and which possesses great mechanical stability underadverse conditions of operation.

An additional object is to provide a delay line which avoids thedisadvantages of rectangular symmetry.

in general, the present invention consists of a polygonal 0r polyhedralstructure having approximately the shape of either a circular disc or asphere, modified to provide a plurality of surfaces for multiplereflection of the sound beam. The structure may be either a solid or acontainer filled with a suitable fluid propagation medium. Either two orthree dimensional paths may be used in both the spherical and circularstructures. For purposes of explanation, however, the embodimentsutilizing a solid thin polygonal structure and two or three dimensionalpaths will be described.

In general, the number of facets on the polygon is odd or a multiple offour, the top and bottom surfaces being left flat. Except for the caseof pairs of facets carrying the generating and receiving transducers,each of the facets makes equal angles with those adjacent thereto and isnormal to the top and bottom polygon surfaces. The facets on which thetransducers are mounted are maintained normal to the top and bottomsurfaces of the polygon, but are tilted through an angle of int/4 fromthe position which would be found in an entirely regular polygon where ais the angle between adjacent reflecting facets and is equal to 21r/n,where n=the total number of facets. Although it is convenient toconstruct the invention from stock of circular crosssection shaped intoa regular polygon (except for the facets on which the transducers aremounted) this feature is not necessary and the polygon need not beregular but the angles between facets must be as defined above. Thus, ingeneral, the angles between adjacent facets are always small integralmultiples of 06/4. For a better understanding of the invention, togetherwith other and further objects, features, and advantages, refer enceshould be made to the following description which is to be read inconnection with the accompanying drawings in which:

Fig. 1 is' a perspective schematic view of one embodiment of the delayline; and

Fig. 2 is a section viewofa second embodiment of the invention.

The embodiment shown in Fig. 1 comprises a thin regular polygon 29of-solid material such as quartz, flat on its top and bottomsurfaces andhaving a series of facets A through I on its perimeter as 'shownin thedrawing. For convenience the over-all structure will be referred to aspolygonal. The polygonal structure is modified as shown to providebilaterally symmetrically placed transducer facets A and F, the detailsof which will be found below. Facet A has a crystal transducer 21mounted thereon and is normal to the top and bottom polygon surfaces,and makes an angle of or with facet B and A a with facet I. Facet F hasmirror symmetry with facet A making an angle of A a. with facet E and awith G. Facet F also has a transducer 22 mounted thereon. The remainingfacets B, .C, D, E, G, H, and l are hereinafter calledregular facetssince each is normal to the top and bottom surfaces of polygon 20 and atan angle a with respect toadjacent regular facets.

When electrical energy is introduced into the transducer 21 mounted onfacet -A, an acoustical wave will be set up which will trace a path tofacet E, which is along the normal to the center of facet A. The energyimpinging on facet B will be incident thereon at an angle of 90/:1degrees to the normal erected at the center of facet E and will bereflected at an angle to this normal which is equal to the incidentangle. The result is that a path will then be traced to facet 1. Anotherreflection similar to the first will occur at this facet and a path willbe traced to facet D. The process continues and a path is tracedsuccessively to facets H, C, G, B, and F, as shown by the dashed linesof Fig. 1. Since facet F is tilted, as noted hereinabove, energyincident on that facet will strike this facet along the normal and willbe either reflected back toward facet B, or, preferably, absorbed inexciting the transducer mounted on facet F.

The embodiment shown in Fig. 1 includes a regular polygon, and itsoperation has'been described in terms of relating to a regular polygonfor the sake of convenience of illustration. Irregular polygons may alsobe used, and the operation thereof would be similar to that of theregular polygonal structure. Also, the path may be terminated at facetsother than F with appropriate tilting of the terminating facet.

The embodiment of the invention illustrated in Fig. 2 is essentially asectional view of Fig. 1 taken along the beam path from A to E, exceptfor two modifications. The facets on the perimeter of the structure ofFig. 2, except for those facets on which the transducers for introducingand extracting energy are mounted, for example, A, are normal to the topand bottom surfaces of the structure. Also, as in. Fig. 1, these facetsmake angles of 360/ n with adjacent facets. In other words, a plan viewof the embodiment of Fig. 2 would be practically identical to the viewof 'Fig. 1. However, the facets on which the transducers are mounted arenot only tilted in one plane at an angle of 06/4 to the normal facetdirection of a regular polygon (as in Fig. l) but, further, the plane isrotated about its top edge through an angle of 45 Hence, the facet liesin a plane which is at an angle of 45 to the top and bottom surfaces ofthe structure and at an angle of :m/ 4 to the usual facet direction.Thus, the beam of energy in this embodiment, starting at A, follows thesame projection in a plane parallel to the top and bottom surfacesbetween facets as the beam in Fig. 1, but each leg of the energy path,for example, A to E in Fig. 2, includes, in addition, a series ofreflections from the top and bottom surfaces caused by the introductionof the energy at the 45 angle. The energy is then reflected at a solidangle from the facet E in a direction towards a facet corresponding to Iof Fig. 1, but again beingreflected from the bottomand top surfacestracing a psmsrmsartstheipsm A? to .E' previously described. Thisprocess "continues until the beam has been reflected from .all theregular facets and arrives normal to the second 45 facet on which thereceiving transducer is mounted. The energy is then absorbed by thetransducer and transmitted to further electrical apparatus. Oneadvantage of this design is that the delay obtained is multiplied by1.414 over the design of Fig. l.

The foregoing description relates only to a simple form of the presentinvention. It is, of course, understood that a polyhedrai structurehaving facets on the surface thereof, or either polygonal or polyhedralstructures having reflecting facets curved to provide focusing of thebeam as it is reflected are within the scope of the present invention.

The invention described herein may be manufactured and used by or forthe Government of the United States of America for governmental purposeswithout the payment of royalty thereon or therefor.

What is claimed is:

1. An ultrasonic delay line comprising, a regular polygonal fused quartzpropagation medium having it facets on the edge thereof, it being an oddinteger, all of said facets lying in planes normal to the top and bottomsurfaces of said medium, two of the facets lying in planes at an angleof /11 to radii to the points of tangency between said polygon and theinscribed circle of said polygon, the remaining facets being located inplanes normal to radii to the points of tangency between said polygonand the inscribed circle of said polygon.

2. Au ultrasonic delay line comprising, a propagation medium havingcharacteristics substantially the same as those of fused quartz andformed into a flat polygon having 11 facets on the edge thereof, Itbeing a multiple of 4, all of said facets lying in planes normal to thetop and bottom surfaces of said flat polygon, two of the facets lying inplanes at an angle of 90/ rz to radii to the points of tangency betweensaid polygon and the inscribed circle of said polygon, the remainingfacets being disposed s'uch that they lie in planes normal to radii tothe points of tangency between said polygon and said inscribed circle.

3. An ultrasonic delay line comprising a solid propagation medium havingcharacteristics similar to those of fused quartz in the form of a flatprism having in facets with top and bottom surfaces parallel, all ofsaid facets lying in planes normal to the top and bottom surfaces ofsaid prism, the angle between any two of m-2 of said facetscorresponding'to r times those of a regular polygon with n sides, or360r/n, where r is an integer less than n, and n is an odd integer equalto or greater than m, while the angle between either of the two exceptedfacets and any one of the m-2-others is 90(4r:1)/n, first and secondcrystal transducers respectively mounted on said two facets, means forapplying an electrical signal to said first crystal transducer, andmeans connected to said second transducer for receiving a signaltherefrom.

4. Anultrasonic delay line comprising a propagation medium having thecharacteristics of fused quartz in the found a flat prism having mfacets with top and bottom surfaces parallel, all of said facets lyingin plane normal to the top and bottom surfaces of said prism, the anglebetween auytwo of m-2 of said facets corresponding to r times those of aregular polygon with n sides, or 360r/n, where r is an integer less thann, and n is a multiple of 4 equal to or greater than m, while the anglebetween either of the two excepted facets and anyone of the 'm2 othersis 90(4r:L-l)/n, first and second crystal transducers respectivelymounted on said two facets, means for applying an electrical signal tosaid first crystal transducer, and means connected to said secondtransducer for receiving a signal therefrom.

5. An ultrasonic delay line comprising a solid propagation medium havingthe characteristics of fused quartz in the form of a flat prism havingin facets with top and bottomj'surfaces. parallel, all of said facetslying in planes normal to the top and bottom surfaces of said prism,

- '5 the angle between any two of m2 of said facets corre sponding to rtimes those of a regular polygon with n sides, or 360 r/n, where r is aninteger less than n, and n is an odd integer equal to or greater than m,while the angle between either of the two excepted facets and any one ofthe m2 others is 90 (4r:1)/n, a first crystal transducer mounted on oneof said two excepted facets, means for applying an electrical signal tosaid first crystal transducer, a second crystal transducer mounted onthe other of said two excepted facets, and means connected to saidsecond crystal transducer for receiving a signal therefrom.

6. An ultrasonic delay line comprising a propagation medium havingsubstantially the characteristics of fused quartz in the form of a fiatprism having in facets with corresponding to 1' times those of a regularpolygon with n sides, or 360 r/ n, where r is an integer less than n,and n is a multiple of 4 equal to or greater than 112, while the anglebetween either of the two excepted facets and any one of the m2 othersis 90 (4ri1)/n, a first crystal transducer mounted on one of said twofacets, means for applying an electrical signal to said first crystaltransducer, a second crystal transducer mounted on the other of said twofacets, and means connected to said sec ond crystal transducer forreceiving a signal therefrom.

7. An ultrasonic delay line comprising, a flat prism having m facetswith top and bottom surfaces parallel, all

of m2 of said facets corresponding to r times those of a regular polygonwith n sides, or 360 r/n, where r is an integer less than n, and n is anodd integer equal to or greater than m, while the angle between eitherof the two excepted facets and any one of the m2 others is 90 (4r:l)/n,first and second crystal transducers, said first crystal transducerbeing mounted on said first facet for directing an ultrasonic wavesubstantially across said polygon to a second of said facets, saidsecond facet resecond crystal transducer for receiving a signaltherefrom. 8. An ultrasonic delay line comprising, a flat prism having mfacets with top and bottom surfaces parallel, all

of m2 of said facets corresponding to r times those of a regular polygonwith n sides, or 360 r/n, where r is an integer less than n, and n is amultiple of 4 equal to or greater than m, while the angle between eitherof the two excepted facets and any one of the m2 others is 90 (4r:l)/n,first and second crystal transducers, said first crystal transducerbeing mounted on said first facet for directing an ultrasonic wavesubstantially across said polygon to a second of said facets, saidsecond facet reflecting said ultrasonic wave substantially across saidpolygon to a third of said facets, similar reflections continuingsuccessively until the ultrasonic wave impinges on said m facet, saidsecond crystal transducer being mounted on said m facet, and meansconnected to said second crystal transducer for receiving a signaltherefrom.

9. An ultrasonic delay line comprising, a flat prism having m facetswith top and bottom surfaces parallel, m2 of said facets lying in planesnormal to the top and bottom surfaces of said prism, the angle betweenany two of m2 of said facets corresponding to r times those of a regularpolygon with n sides, or 360 r/n, where r is an integer less than n, andn is an odd integer equal to or greater than m, while the angle betweeneither of the two excepted facets and any one of the m2 others is (4ri-1)/n, first and second crystal trans; ducers, said first crystaltransducer being mounted on said first facet for directing an ultrasonicwave downwardly to: ward the bottom surface of said polygon, the bottomsurface reflecting said' wave to the top surface, successive reflectionscontinuing from the bottom and top surfaces until said wave occurring atsaid second facet, further reflections similar to those between saidfirst and said second facets occurring until said wave impinges on athird of said facets,the process being continued until said waveimpinges on said m facet, said second crystal transducer being mountedon said m facet, and means connected to said second crystal transducerfor receiving a signal therefrom.

10. An ultrasonic delay line comprising, a flat prism having 212 facetswith top and bottom surfaces parallel, m2 said facets lying in planesnormal to the top and bottom surfaces of said prism, the angle betweenany two of m2 of said facets corresponding to r times those of a regularpolygon with n sides, or 360 r/n, where r is an integer less than n, andn is a multiple of 4 equal to or greater than m, while the angle betweeneither of the two excepted facets and any one of the m2 others is 90(4r1-1)/n, first and second crystal transducers, said first crystaltransducer being mounted on said first facet said wave occurring at saidsecond facet, further reflecfacets, the process being continued untilsaid wave impinges on said m facet, said second crystal transducer beingmounted on said m facet, and means connected to said second crystaltransducer for receiving a signal therefrom.

11. An ultrasonic delay line comprising a propagation medium having morethan 6 surfaces, at least 5 of said and second electro-acousticaltransducers, said transducers mounted in contact with first and secondperimetrical surfaces, respectively, means for applying an electricalsignal to one of said transducers whereby a beam of acoustical energy isdirected through said medium to a third surface and reflected therefromto another of said surfaces, further reflections occurring until saidacoustical energy impinges on said second surface having the secondtransducer, and means connected to said second transducer for receivinga signal therefrom.

12. An ultrasonic delay line of the type described in claim 11 whereinthe surfaces are plane surfaces.

13. An ultrasonic delay line of the type described in claim 11whereinthe propagation medium is a solid.

medium, each of said other surfaces comprising said polygonal perimeterbeing at an angle other than 90 with at least one immediately adjacentsurface of said other surfaces comprising said polygonal perimeter, saidother surfaces extending between said 2 parallel surfaces, first andsecond electro-acoustical transducers, said transtucers mounted incontact with first and second perimetrical surfaces, respectively, meansfor applying an electrical signal to one of said transducers whereby abeam of acoustical energy is directed through said medium to a thirdsurface and reflected therefrom toward another of said surfaces, furtherreflections occurring until said acoustical energy impinges on saidsecond surface having said .second transducer, and means connected tosaid second transducer for receiving a signal therefrom.

15. An ultrasonic delay line of the type defined in claim 14 wherein thepropagation medium is a solid.

16. An ultrasonic delay line of the type defined in claim 14 wherein theperimetrical surfaces are normal to the 2 parallel surfaces.

17. An ultrasonic delay line of the type defined by claim 14 wherein theperimetrical surfaces on which the transducers are mounted are notnormal to the two parallel surfaces.

18. An ultrasonic delay line comprising a polygonal fused quartzpropagation medium having it facets between top and bottom surfacesthereof, 11 being an integer at least equal to live, two of said'facetslying in planes at an angle of 90/n to radii to the points of tangencybetween said polygon and the inscribed circle of said polygon, theremaining facets being located in planes normal to radii to the pointsof tangency between said polygon and the inscribed circle of saidpolygon.

19. An ultrasonic delay line comprising a solid propagation medium inthe form of a flat prism having in facets with top and bottom surfacesparallel, all of said facets lying in planes normal to the top andbottom surfaces of said prism, the angle between any two of m-2 of saidfacets corresponding to 1' times those of a regular polygon with nsides, or 360r/n, where r is an integer less than a and n is an integerequal to or greater than in, while the angle between either of the twoexcepted facets and any one of the ru -2 others is 90 (4ril)/n, firstand second crystal transducers respectively mounted on said two facets,means for applying an electrical signal to said first crystaltransducer, and means connected to said second transducer for receivinga signal therefrom.

20. An ultrasonic delay line comprising a propagation medium having areflecting facets disposed between the top and bottom surfaces andcomprising a. polygonal perimeter of said delay line, a being an integerat least equal to five, the angular relationships among n-2 of saidfacets conforming substantially to the angular relationships amongcorresponding sides of an equi-angular polygon of at least it sides, theangular relationshipbetween each of two expected facets and said n2facets differing from the angular relationship between correspondingsides of an equi-angular polygon of at least :2 sides by an amount equalto a multiple of /n.

21. The delay line of claim 20 further characterized by transducer meansmounted on said polygonal perimeter for inducing supersonic energywithin said delay line, whereby said energy is multiply reflected fromsaid facets.

22. An ultrasonic delay line comprising a propagation medium having 11reflecting facets disposed between top and bottom surfaces andcomprising a polygonal perimeter of said medium, 11 being an integer atleast equal to five, the angular relationships among 11-2 of said facetsconforming substantially to the angular relationships amongcorresponding sides of an equi-angular polygon of at least it sides, theexcepted two facets being tilted through an angle equal to lit/4 fromthe position they would occupy if said It facets formed an equi-angularpolygon, where a is the angle between adjacent sides of an equi-angularpolygon of at least n sides.

23. The ultrasonic delay line of claim 22 further characterized by firstand second transducer means mounted on said first and second ones ofsaid reflecting facets, means connected to said first transducer meansfor applying an electrical signal to said transducer means, and

means connected to said second transducer means for receiving a signaltherefrom.

References Cited in the file of this patent 1 UNITED STATES PATENTS2,472,600 Luboshez June 7, 1949 2,505,364 McSkimin Apr. 25, 19502,505,515 Arenberg Apr. 25, 1950 2,525,861 Carlin Oct. 17, 19502,540,720 Forbes Feb. 6, 1951 2,624,804 Arenberg Ian. 6, 1953

